Thermostatically controlled electric cooker hot plate

ABSTRACT

An electric cooker hot plate has an insert for securing a temperature senser to contact the bottom of a cooking vessel placed on the hot plate. The hot plate has an opening in a central unheated portion. The insert has a thin peripheral wall by which the insert is fitted in the bore. The upper rim of the insert is peened over into a recess in the hot plate central portion. The lower end portion of the insert is enlarged and depends below the hot plate. The insert is thereby securely locked in position.

United States Patent Fischer et a1.

[54] THERMOSTATICALLY CONTROLLED ELECTRIC COOKER HOT PLATE [72] Inventors: Karl Fischer; Felix Schreder, both of Oberderdingen, Germany [73] Assignee: Mssrs. E. G. O. Elektro-Gerate Blane u. Fischer, Oberderdingen, Germany [22] Filed: March 16, 1971 [21] Appl.No.: 124,830

[52] US. Cl. ..219/450, 29/512, 85/78, 219/433, 219/452, 219/459 [51] Int. Cl. ..H05b 3/68 [58] Field of Search ..219/448-49, 450, 219/451-52, 458, 459, 462, 464, 441, 432,

[56] References Cited UNITED STATES PATENTS 3/1957 Weber et a1. ..219/450 1/1962 Kelly ..219/450 X 9/1965 Barry ..29/512 X 11/1965 Dupree ..85/50 [15] 3,684,862 51 Aug. 15, 1972 3,235,709 2/1966 Fischer ..219/450 3,292,482 12/1966 Fry et a1. ..85/78 3,369,289 2/1968 Gapp ..29/512 FOREIGN PATENTS OR APPLlCATlONS 388,483 6/1965 Switzerland ..219/450 975,526 11/1964 Great Britain ..219/450 1,000,367 8/ 1965 Great Britain ,.2l9/450 1,161,931 8/1969 Great Britain ..219/450 Primary ExaminerVolodymyr Y. Mayewsky Attorney-Brumbauch, Graves, Donohue & Raymond [5 7] ABSTRACT An electric cooker hot plate has an insert for securing a temperature senser to contact the bottom of a cooking vessel placed on the hot plate. The hot plate has an opening in a central unheated portion. The insert has a thin peripheral wall by which the insert is fitted in the bore. The upper rim of the insert is peened over into a recess in the hot plate central portion. The lower end portion of the insert is enlarged and depends below the hot plate. The insert is thereby securely locked in position.

17 Claims, 3 Drawing Figures PATENTEDAm; 15 1912 SHEET 1 0F 2 INVENTOR.

THERMOSTATICALLY CONTROLLED ELECTRIC COOKER HOT PLATE The invention relates to electrical hot plates and more particularly to an electrical hot plate having an unheated central zone with an opening in which is fitted an insert having a thin-walled sleeve-like periphery. Such an insert normally serves to receive a temperature sensor. The insert may be of closed construction, i.e., of inverted cup-shaped construction, the temperature sensor being arranged within the insert. Alternatively, however, the insert may have a central opening through which a temperature sensor bulb projects upwardly. The temperature sensor bulb is arranged resiliently in the insert such that it can abut against the bottom of the cooking vessel. The temperature sensor usually comprises a bulb filled with an expansible fluid and connected to a corresponding regulator by way of a capillary tube.

A known insert for an unheated central zone of a hot plate has a bottom flange by which the insert is secured to the underside of the hot plate by means of screws. The same screws secure to the hot plate a stop plate which is engaged by resilient stop elements of the carrier for the sensor bulb.

A feature of the invention is to provide for an electrical cooker hot plate an insert which is simple to manu facture and mount and, even under extreme conditions, avoids defects resulting from liquid running through i the opening.

In accordance with the invention, the insert is pressed into the hot plate opening and has in the region of the top of the hot plate a peened-out portion which is produced by cold deformation and which projects laterally beyond the shell and is located in a recess at the edge between the opening and the top of the hot plate, and the thin peripheral wall of opening insert has a widened portion in the region of the bottom rim of the opening and projects downwardly beyond the bottom rim.

The insert can be reliably secured to the cooking plate by virtue of the peened-out portion. Additional fixing by means of screws is not required. Furthermore, when forming the peened-out portion, the widened portion, which is preferably conical, in the region of the bottom rim of the opening is drawn slightly into the opening, so that stresses are built in at this location and ensure good sealing. The insert is not only pressed against the opening in the radial position, but is also axially clamped, so that additional contact pressure in the rim regions is obtained when the hot plate expands under heat.

In a method for mounting an insert in an electric hot plate, in accordance with the invention, the insert, whose upper peripheral region is cylindrical and which is provided with a widened portion in its bottom region, if pressed into the opening by means of a punch which supports the insert from the inside and also from the outside in the region located below the hot plate, the peened-out portion being formed out bymeans of a counter-punch. After removal of the punch a ring can be slipped on and secured to the peripheral wall by spot welding.

The invention is further described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a cross section through the central zone of an electric cooker hot plate fitted insert constructed in accordance with the invention, drawn to a greatly enlarged scale,

FIG. 2 is a section, corresponding to FIG. 1, of a variant of an insert, and

FIG. 3 is an illustration, similar to FIG. 2, of a further variant.

Referring to FIG. 1, a cylindrical opening 12 is located in the central unheated portion of an electric hot plate 11 made from cast material. The rims of the opening 12 are provided with chamfers 15, 16 on the top 13 and the underside 14 of the hot plate. Heating elements 17 of the hot plate are fitted into grooves (not illustrated) and are surrounded by a pressed-in insulating composition 17.

In the embodiment illustrated in FIG. 1, an insert 18 made from a thin-walled material, such as stainless sheet steel, is mounted in the opening 12. The insert 18 has a cylindrical peripheral wall 19 which abuts against the opening 12 with a press fit. The top region of the insert has a continuous, lateral peened-out portion 20 which lies in a recess formed by the chamfer 15. The insert extends inwardly from the peened-out portion 20 to form a flange 21 which is slightly offset downwardly or dished. The central region of the insert has a circular opening 22 for receiving a sensor bulb 31 which is to be pressed byspring force against the cooking vessel resting on the top of the hot plate.

The insert has a conical widened portion 23 in the region of the underside 14 of the hot plate 11, which widened portion 23 is normally drawn slightly into the cylindrical region of the opening 12. A cylindrical portion 24 of the insert is contiguous to the conical widened portion 23. The cylindrical portion 24 and a portion of the widened portion 23 are surrounded by a ring 25 located at a distance therefrom. The inside of the ring 25 has several corrugations 26 which extend inwardly substantially up to the cylindrical portion 24 and are connected thereto by spot welding. Alternatively, projections other than corrugations may be used. Any liquid which leaks through is drained off downwardly by means of a drainage channel 27 formed between the cylindrical portion 25 and the ring 25. The top end face 28 of the ring 25 abuts against the underside 14 of the hot plate, and the bottom end face of the ring is provided with an inwardly directed flange 29 on which are located two locking elements 30. The locking elements 30 serve to receive resilient stop elements on a carrier 32 (illustrated by dash-dot lines) which supports and presses against a sensor bulb 31. Thus, the ring 25 has a double function.

The insert is mounted on the hot plate 11 in the following manner. The sleeve is manufactured without the peened-out portion 20 and is received by a punch which inwardly supports the thin peripheral wall region 19 of the insert, the widened portion 23 and the cylindrical portion 24, and outwardly surrounds the portion 24. The peripheral wall region 29 initially has a diameter exceeding that of the opening 12 by a few tenths of a millimeter. The insert is pressed into the opening 12 by means of the punch, the relatively thin-walled material of the insert being satisfactorily guided in its bottom region and being protected against deformation or buckling. The peened-out portion 20 is then formed from above by means of a counter-tool and is laid into the chamfering and thus forms a positive retaining means for the insert. The widened portion 23 is drawn slightly into the cylindrical portion of the bore 12 during the pressing-in operation, so that, in addition to the actual press fit, resilient pressure occurs in the bottom region of the opening 12. This is particularly favorable, since the lowest temperature of the hot plate normally prevails in this region where the greatest margin of safety thus exists with differences in expansion, so that tightness can be ensured.

After the punch has been removed, the ring 25 provided with the corrugations 26 is slipped over the cylindrical portion 24 until the ring abuts against the underside .14 of the hot plate and it is then secured to the cylindrical portion 24 by spot welding. Thus, the insert is additionally positively fixed to the hot plate.

It will be appreciated that this insert is extremely tight at its rim region even when the plate and the insert are subjected to the greatest temperature stresses. If, contrary to expectation, liquid should leak through in the rim region, the ring 25 serves to ensure that it cannot flow further towards the insulating composition 17. On the contrary, the liquid present in the region of the chamfer 16 is diverted downwardly by the capillary action in the drainage channel 27 between the ring 25 and the cylindrical portion 24 and is carried away on the insert in a capillary manner. These measures substantially avoid any danger to the electrical parts of the hot plate. The fact that the portion 24 of the insert 18 extends downwardly beyond the underside of the hot plate ensures that fluid running down the outside and the inside of the insert can drip off without running into the insulating composition 17.

FIG. 2 shows an insert 18 which is of substantially the same construction as the insert 18 illustrated in FIG. 1. However, the insert 18' has a fully closed top surface 33 contiguous to the peened-out portion and flush with the top surface of the hot plate 11. In this case, the temperature sensor can be accommodated below the surface 33, Le, completely sealed from liquid spilling onto the top of the hot plate. Instead of the ring 25, the insert 18 has a ring 35 which is fitted inside the portion 24 of the insert and secured thereto, e.g., by welding. The temperature sensor (not illustrated in this FIG. can abut against inwardly directed flan ge-like portions 36 on the underside of the ring 35.

FIG. 3 shows a further variant which, with the exception of the construction of the top, is identical to the insert 18' illustrated in FIG. 2. The insert 18" has an inwardly directed flange 37 which is contiguous to the peened-out portion 20 and which defines an opening. This opening is closed by a plate 38 which is secured by a rim 39 to the flange 37 from below, for example by welding.

The central region of the plate 38 projects upwardly to an extent where it is substantially flush with the flange 37 which is itself flush with the upper surface of the hot plate 11. This construction has the advantage that the material in the top region of the insert can be of optional thickness, so that, when a thicker material has been selected for the insert for reasons of strength for example, the plate is of thinner construction in order to prevent dissipation of the heat to be conducted to the temperature sensor located below the plate.

Furthermore, this can prevent the top portion of the insert from bulging upwardly or downwardly with the great variations in temperature occurring.

Whilst all three embodiments are shown as having a lower conical widened portion, the widening may be achieved in other ways, e.g., by continuous peripheral external corrugation.

We claim:

1. In an electric hot plate having an electric heating element, an unheated central zone with an opening therein and a temperature sensor bulb arranged in said opening, the improvement comprising: I) an insert in said opening, said insert having a thin peripheral wall by which the insert is pressed into said opening, a coldformed peened-out insert portion in the region of the top of the hot plate and lying in a recess at the juncture between the opening and the top of the hot plate, said peened-out portion projecting laterally beyond the peripheral wall of the insert, a widened insert portion in the lower region of main insert peripheral wall and depending downwardly beyond the bottom of the hot plate, and an inwardly directed flange in the region of the top of the hot plate, said inward flange adjoining said peened-out portion and surrounding a central opening formed in said insert, and insert being adapted to receive said temperature sensor bulb resiliently secured therein; and (2) a ring inserted into the depending insert portion and having therein inwardly directed portions for holding said temperature sensor bulb.

2. The apparatus according to claim 1, in which said ring has thereon a locking element for resilient engagement of a carrier for said temperature sensor bulb.

3. The apparatus according to claim 1, in which the top of the insert is closed.

4. The apparatus according to claim 1, in which said recess in said hot plate is a circumferentially continuous chamfer.

5. The apparatus according to claim 1, in which said lower insert peripheral wall portion is conical.

6. The apparatus according to claim 1, in which said lower insert peripheral wall portion has a continuous corrugation thereon.

7. The apparatus according to claim 1, in which said insert has thereon in the region of the top of the hot plate an inwardly directed flange which adjoins the peened-out portion and defines a central opening in said insert and in which a plate is mounted on said flange to close said insert opening.

8. In an electric hot plate having an electric heating element, an unheated central zone with an opening therein and a temperature sensor bulb arranged in said opening, the improvement comprising: (1) an insert in said opening, said insert having a thin peripheral wall by which the insert is pressed into said opening, a coldfonned peened-out insert portion in the region of the top of the hot plate and lying in a recess at the juncture between the opening and the top of the hot plate, said peened-out portion projecting laterally beyond the peripheral wall of the insert, a widened insert portion in the lower region of said insert peripheral wall and depending downwardly beyond the bottom of the hot plate, and an inwardly directed flange in the region of the top of the hot plate, said inward flange adjoining said peened-out portion and surrounding a central opening formed in said insert, said insert being adapted to receive said temperature sensor bulb resiliently secured therein; and (2) a ring surrounding the portion of the insert projection downwardly from the opening, a drainage channel being defined between the ring and the insert.

9. The apparatus according to claim 8 wherein said ring has internal projections which engage said lower depending insert portion and are welded thereto.

10. The apparatus according to claim 8, in which the top end face of said ring abuts against the underside of the hot plate.

11. The apparatus according to claim 8, in which the lower edge of said opening has a chamfer thereon in the region of said drainage channel.

12. The apparatus according to claim 8, in which said ring has thereon a locking element for resilient engagement of a carrier for said temperature sensor bulb.

13. The apparatus according to claim 8, in which the top of the insert is closed.

14. The apparatus according to claim 8, in which said recess in said hot plate is a circumferentially continuous chamfer.

15. The apparatus according to claim 8, in which said lower insert peripheral wall portion is conical.

16. The apparatus according to claim 8, in which said lower insert peripheral wall portion has a continuous corrugation thereon.

17. The apparatus according to claim 8, in which said insert has thereon in the region of the top of the hot plate an inwardly directed flange which adjoins the peened-out portion and defines a central opening in said insert and in which a plate is mounted on said flange to close said insert opening. 

1. In an electric hot plate having an electric heating element, an unheated central zone with an opening therein and a temperature sensor bulb arranged in said opening, the improVement comprising: (1) an insert in said opening, said insert having a thin peripheral wall by which the insert is pressed into said opening, a cold-formed peened-out insert portion in the region of the top of the hot plate and lying in a recess at the juncture between the opening and the top of the hot plate, said peened-out portion projecting laterally beyond the peripheral wall of the insert, a widened insert portion in the lower region of main insert peripheral wall and depending downwardly beyond the bottom of the hot plate, and an inwardly directed flange in the region of the top of the hot plate, said inward flange adjoining said peened-out portion and surrounding a central opening formed in said insert, and insert being adapted to receive said temperature sensor bulb resiliently secured therein; and (2) a ring inserted into the depending insert portion and having therein inwardly directed portions for holding said temperature sensor bulb.
 2. The apparatus according to claim 1, in which said ring has thereon a locking element for resilient engagement of a carrier for said temperature sensor bulb.
 3. The apparatus according to claim 1, in which the top of the insert is closed.
 4. The apparatus according to claim 1, in which said recess in said hot plate is a circumferentially continuous chamfer.
 5. The apparatus according to claim 1, in which said lower insert peripheral wall portion is conical.
 6. The apparatus according to claim 1, in which said lower insert peripheral wall portion has a continuous corrugation thereon.
 7. The apparatus according to claim 1, in which said insert has thereon in the region of the top of the hot plate an inwardly directed flange which adjoins the peened-out portion and defines a central opening in said insert and in which a plate is mounted on said flange to close said insert opening.
 8. In an electric hot plate having an electric heating element, an unheated central zone with an opening therein and a temperature sensor bulb arranged in said opening, the improvement comprising: (1) an insert in said opening, said insert having a thin peripheral wall by which the insert is pressed into said opening, a cold-formed peened-out insert portion in the region of the top of the hot plate and lying in a recess at the juncture between the opening and the top of the hot plate, said peened-out portion projecting laterally beyond the peripheral wall of the insert, a widened insert portion in the lower region of said insert peripheral wall and depending downwardly beyond the bottom of the hot plate, and an inwardly directed flange in the region of the top of the hot plate, said inward flange adjoining said peened-out portion and surrounding a central opening formed in said insert, said insert being adapted to receive said temperature sensor bulb resiliently secured therein; and (2) a ring surrounding the portion of the insert projection downwardly from the opening, a drainage channel being defined between the ring and the insert.
 9. The apparatus according to claim 8 wherein said ring has internal projections which engage said lower depending insert portion and are welded thereto.
 10. The apparatus according to claim 8, in which the top end face of said ring abuts against the underside of the hot plate.
 11. The apparatus according to claim 8, in which the lower edge of said opening has a chamfer thereon in the region of said drainage channel.
 12. The apparatus according to claim 8, in which said ring has thereon a locking element for resilient engagement of a carrier for said temperature sensor bulb.
 13. The apparatus according to claim 8, in which the top of the insert is closed.
 14. The apparatus according to claim 8, in which said recess in said hot plate is a circumferentially continuous chamfer.
 15. The apparatus according to claim 8, in which said lower insert peripheral wall portion is conical.
 16. The apparatus according to claim 8, in which said lower insert peripheral wall portion Has a continuous corrugation thereon.
 17. The apparatus according to claim 8, in which said insert has thereon in the region of the top of the hot plate an inwardly directed flange which adjoins the peened-out portion and defines a central opening in said insert and in which a plate is mounted on said flange to close said insert opening. 